I. Technical Field
The present invention relates to an angular velocity sensor element used for electronic equipment, an angular velocity sensor having the element, and an angular velocity sensor unit. It also relates to a method of detecting a signal of the angular velocity sensor element.
II. Description of the Related Art
FIG. 23 is a top view showing a conventional angular velocity sensor element. In FIG. 23, a pair of arms 1002a and a pair of arms 1002b extend in a crosswise direction from holding section 1001 as the center. In each pair, the arms are symmetrically disposed. The pair of arms 1002a is detecting arm 1002a, whereas the pair of arms 1002b is supporting arm 1002b. Driving arm 1003 is disposed on the tip of supporting arm 1002b. When driving arm 1003 is vibrated in the directions indicated by the arrows, angular velocity is produced and the Coriolis force is exerted on driving arm 1003. The Coriolis force accompanies a stress that is exerted on supporting arm 1002b and then transmitted to detecting arm 1002a, by which detecting arm 1002a vibrates in the directions indicated by the arrows. The vibration causes a deflection in detecting arm 1002a and the deflection is electrically converted into an output signal. The angular velocity sensor element described above is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2003-337025.
However, the aforementioned angular velocity sensor element has a cantilever structure where the center part of driving arm 1003 is fixed to supporting arm 1002b. In the structure above, vibration velocity greatly differs between the tip of driving arm 1003 and the tip of supporting arm 1002b fixed to the center of driving arm 1003 as the base point of vibration. The Coriolis force occurs in proportion to the vibration velocity. It is therefore difficult to obtain the Coriolis force at around the base point of vibration of driving arm 1003, resulting in poor stress to be transmitted to detecting arm 1002a. 
FIG. 24 is a top view showing another structure of a conventional angular velocity sensor element. In FIG. 24, crystal-made holding section 2001 of a square shape has first arm 2002 and second arm 2003 extending in an X-axis direction. First detecting electrode vibrating body 2004 is made of crystal. One end of vibrating body 2004 is connected to holding section 2001 and the other end extends in a Y-axis direction. First detecting electrode vibrating body 2004 has four outside surfaces and each of which has detecting electrode 2005 thereon. Besides; holding section 2001 has second detecting electrode vibrating body 2006 in the Y-axis direction on the opposite side of first detecting electrode vibrating body 2004. Similarly, second detecting electrode vibrating body 2006 has four outside surfaces and each of which has detecting electrode 2005 thereon.
First driving electrode vibrating body 2007 is made of crystal. One end of vibrating body 2007 is connected to first arm 2002 and the other end extends in the Y-axis direction. First driving electrode vibrating body 2007 has four outside surfaces and each of which has detecting electrode 2008 thereon.
Second driving electrode vibrating body 2009 is made of crystal. One end of vibrating body 2009 is connected to first arm 2002 and the other end extends in the Y-axis direction on the opposite side of first driving electrode vibrating body 2007. Second driving electrode vibrating body 2009 has four outside surfaces and each of which has detecting electrode 2008 thereon.
Third driving electrode vibrating body 2010 is made of crystal. One end of vibrating body 2010 is connected to second arm 2003 and the other end extends in the Y-axis direction. Third driving electrode vibrating body 2010 has four outside surfaces and each of which has detecting electrode 2008 thereon.
Fourth driving electrode vibrating body 2011 is made of crystal. One end of vibrating body 2011 is connected to second arm 2003 and the other end extends in the Y-axis direction on the opposite side of third driving electrode vibrating body 2010. Fourth driving electrode vibrating body 2011 has four outside surfaces and each of which has detecting electrode 2008 thereon.
The conventional angular velocity sensor element has the structure described above. Next, the workings of the sensor element will be described.
When AC voltage is applied to each driving electrode 2008 of first driving electrode vibrating body 2007, second driving electrode vibrating body 2009, third driving electrode vibrating body 2010, and fourth driving electrode vibrating body 2011, the aforementioned four vibrating bodies vibrate in a driving direction at velocity V. When the angular velocity sensor element is rotated, at angular velocity ω, on a Z-axis that is perpendicular to the plane on which the angular velocity sensor element is disposed, first driving electrode vibrating body 2007, second driving electrode vibrating body 2009, third driving electrode vibrating body 2010, and fourth driving electrode vibrating body 2011 undergo Coriolis force F (=2mv×ω). Transmitting the Coriolis force, via first arm 2002, second arm 2003 and holding section 2001, to first detecting electrode vibrating body 2004 and second detecting electrode vibrating body 2006 allows each detecting electrode 2005 to output an output signal corresponding to angular velocity. Such structured sensor element is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2001-264067.
See also Japanese Unexamined Patent Application Publication No. 2006-275878.
In the conventional structure above, however, each one end of first driving electrode vibrating body 2007 and second driving electrode vibrating body 2009 is fixed to first arm 2002; similarly, each one end of third driving electrode vibrating body 2010 and fourth driving electrode vibrating body 2011 is fixed to second arm 2003. Therefore, the vibration of the sensor element is peculiar to that of a cantilever structure. Compared to the fixed ends of the four vibrating bodies above, each free end of them has less amount of displacement, and accordingly, a small amount of Coriolis force. As a result, the angular velocity sensor element has low sensibility of output.